Searching in Rust Language (#1172)

* Create linear_search.rs

* Create binary_search_tree.rs

* Create binary_search.rs

searching/binary_search/rust/binary_search.rs

@@ -0,0 +1,44 @@
+
+const BLOCK_SIZE: usize = 128;
+
+// Binary search over an array of 128 els.
+// 
+// Returns the first i such that
+// block[i] >= target.
+//
+// # Assumes
+// 
+// That block is sorted, and that the last `doc` in 
+// block is `>= target`.
+// If none of the elements is greater than the last doc, 
+// this function returns 127, which does not make much sense.
+#[inline(never)]
+fn binary_search(block: &[u32; BLOCK_SIZE], target: u32) -> usize {
+    // Full block of 128 els.
+    // 
+    // We do a branchless, unrolled binary search.
+    let mut start = 0;
+    let mut half: usize = BLOCK_SIZE / 2;
+    for _ in 0..7 {
+        let middle = start + half;
+        unsafe {
+            let pivot: u32 = *block.get_unchecked(middle);
+            asm!("cmpl $2, $1\ncmovge $3, $0"
+                 : "+r"(start)
+                 :  "r"(target),  "r"(pivot), "r"(middle))
+                 ;
+        }
+        half /= 2;
+    }
+    start
+}
+
+fn main() {
+    let mut arr = [0u32; 128];
+    for i in 0..128 {
+        arr[i] = i as u32;
+    }
+    for i in 0..129 {
+        println!("{}", binary_search(&arr, i));    
+    }
+}